Method of grinding and aluminum-nickel alloy



- electron emissive coatings,

United States Patent METHOD OF GRINDING AN ALUMINUlW-NICKEL ALLOYLeonard W. Kates, Hempstead, N. Y., assignor to Sylvania ElectricProducts Inc, a corporation of Massachusetts No Drawing. ApplicationSeptember 29, 1955 Serial No. 537,541

2 Claims. (Cl. 106-490) My invention is directed toward methods forproduccarbonates of barium, strontium and calcium. A heater element isinserted within the sleeve. -When the heater is electrically energizedand the cathode is heated to a suitable temperature, electrons areemitted from the layer.

It is known that when a small amount of one or more metal activators isalloyed with the base metal in the sleeve, to form What is known to theart as an active alloy, the resultant cathode is a better electronemitter. See for example my copending application, Serial No. 284,931,filed April 29, 1952, when aluminum is used as an activator. Othermetals such as chromiumand mag nesium are also used as activators.

The electron emissive properties of cathode structures can likewise beimproved by incorporating the active alloy in the electron emissivecoating rather than in the sleeve itself.

This process is particularly advantageous when, for example, the heaterelement is formed from tungsten, for if metal activators areincorporated into the sleeve itself, the cathode structure is adverselyaifected. In particular, the heater-cathode leakage is appreciablyincreased.

In one process for incorporating an active alloy in the an active alloypowder is mixed into a suspension of alkaline earth metal carbonates bygrinding the powder and the suspension together in a ball mill.

Conventional ball mills are lined, for example, with porcelain or silex.The grinding media consists of flint or porcelain pebbles or balls.Consequently, both the grinding media and the mill lining containsilica; and when the active alloy powder and the carbonate suspensionare ground together in this type of ball mill, some of the silica isworn away from the lining and pebbles and is incorporated as an impurityinto the suspension. When such a silicon containing suspension isapplied to the cathode sleeve and subsequently heated to form the finalelectron emissive coating, the silica forms slags and interfacialcompounds which result in impaired emission.

Accordingly, it is an object of the present invention to improve theprocess in which active alloy powders and suspensions of alkaline earthmetal carbonates are ground together in a ball mill in such manner thatno impurities are incorporated into the suspension.

Another object is to provide a new and improved process for grindingactive alloy powders and suspensions of alkaline earth metal carbonatestogether in a ball mill in such manner as to prevent siliconcontamination of the suspension.

Still another object is to provide a new and improved process for ballmilling an active alloy powder into a suspension of alkaline earth metalcarbonates without adding impurities to the suspension.

These and other objects will either be explained or will become apparenthereinafter.

In my invention, a ball mill is lined with the base metal component ofan active metal alloy. The grinding media (for example balls or pebbles)is formed from the alloy itself. A suspension, for example, an aqueoussuspension, of alkaline earth metal carbonates is then ground in theball mill. In the grinding process, some of the active alloy is wornaway from the grinding media and is incorporated into the suspension.Since there is substantially no silica or other similar impurity presentin the lining, grinding media or the suspension itself, the resultantactive alloy bearing suspension is necessarily free from suchimpurities.

in one specific embodiment of my invention, the ball mill is lined withnickel and the grinding media is formed from balls composed of analuminum-nickel alloy, the aluminum being present in an amount ofapproximately 1% by weight.

Alternatively, the ball mill can be lined with the aluminum nickel alloyand the balls can be formed from nickel.

However, since the grinding balls are worn away much more rapidly thanthe lining, and since it is far easier to add additional ballsperiodically rather than to reline the ball mill itself, it ispreferable to have the balls composed of the active alloy and the liningcomposed of the base metal component (nickel) of this alloy.

Obviously, such parameters as the size and composition of the balls, thetypes of carbonate suspensions and the length of the grinding operationcan be varied as necessary in a manner well known to those skilled inthe art.

I have found, however, that an electron emissive coating containingcontrolled amounts of the nickel aluminum alloy and substantially freefrom silica and other similar impurities can be obtained through the useof an active alloy bearing alkaline earth carbonate suspension formed bygrinding conventional aqueous suspension of double or triple carbonatesin a nickel lined ball mill for a period of several hours, the grindingelements being composed of the above described aluminum-nickel alloy andhaving an average diameter of one half inch.

While I have shown and pointed out my invention as applied above, itwill be apparent to those skilled in the art that many modifications canbe made Within the scope and sphere of my invention as defined in theclaims which follow.

References Cited in the file of this patent UNITED STATES PATENTS TaylorJan. 24, 1933 Comstock Apr. 23, 1935 Bouchard Dec. 26, 1950

1. A METHOD FOR ADDING AN ALUMINUM NICKEL ALLOY TO AN AQUEOUSSUSEPENSION CONTAINING AT LEAST ONE ALKALINE EARTH METAL CARBONATE, SAIDMETHOD COMPRISING THE STEP OF CONTACTING SAID SUSPENSION WITH GRINDINGMEDIA IN A BALL MILL, THE INNER SURFACE OF SAID MILL BEING LINED WITHNICKEL, SAID GRINDING MEDIA BEING COMPOSED OF SAID ALLOY.